Conductive polymers are presently known materials. Also, conductive polymers are partly commercially available. They are currently considered as material for integrated circuits, light emitting devices, antistatic materials, displays and batteries.
However, conductive polymers are generally difficult to process and have poor stability, which greatly limits their applicability in various applications. For an application to detect markers in a liquid, the currently available conductive polymers typically exhibit stability problems, as the original physical shape undergoes variations as a consequence of the contact with liquids, particularly at increasing temperature, and in organic solvents. This shape variation causes a variation of the electrical properties and a degradation of the polymer during storage.
On the other hand, it is often desired to verify the origin and authenticity of liquids of various kinds, such as fuels (e.g. diesel, kerosene, gasoline etc.) in order to be able to identify forged or non-genuine products. For this purpose, a marking substance (marker) is often added to the liquid, such as a specific dye. The addition of a marker is also employed in order to distinguish between liquids that are chemically identical or very similar, but which are regulated differently. One example is the addition of a certain dye into heavily taxed diesel fuel in Germany, while the chemically very similar or identical heating oil is taxed at a lower rate and is not marked with a specific dye. The identity of a liquid in a car tank can then be assessed by analyzing the liquid as to presence of the specific marker dye.
The authenticity of the liquid is then assessed by means of a detector, e.g. a colour detector or spectral analysis in case of a certain dye. Yet, often bulky and expensive equipment is needed in order to detect the marker. Further, the marker often needs to be present in significant quantities in order to allow a reliable detection. In another aspect, the marking can be easily counterfeited if commercially available substances (e.g. dyes) are used, as only the properties of the marker (but not its interaction with a detection device) are assessed.